The prime minister, of course, did not make this clear when he made his vow to the Scottish people in the Daily Record along with Nick Clegg and Ed Miliband. He kept silent because he knows the issue is so entangled that it would have diluted his devolution pledge, given at a time when polls were suggesting Scotland might vote yes.

The implications of Scottish MPs being excluded from the Commons on an array of issues is not just a constitutional thicket, but also a crude political nightmare for Miliband, the Labour leader, since he is likely to have rely on a phalanx of Scottish MPs to secure an overall majority for much legislation.

On the face of it, Cameron, in his dawn statement on the steps of Downing Street, said that if issues such as tax and welfare were devolved to Scotland, then Scots MPs would have to be excluded from votes on these issues. If carried through, the pledge raises the question of whether a Scotland-based constituency MP could again be chancellor of the exchequer or vote on the budget. Indeed, one English Conservative MP, Bernard Jenkin, has said a Scottish chancellor must be a thing of the past.

Labour will react warily to the idea, knowing it may seem popular in England and is already being demanded by the UK Independence party (Ukip). But initial reaction from senior Labour figures such as Owen Smith, the shadow Welsh secretary, was hostile. "The last thing Scotland needs is a constitutional fix which reduces Scotland's voice at Westminster & strengthens Tories' grip on power," he tweeted. "Farage and Cameron united today in responding to yesterday's decision by seeking to concentrate more power in their hands & at Westminster," he added.

The political threat to Labour from English votes for English laws is not clear cut. Research by My Society shows only 21 votes of more than 3,000 since 1997 would have gone differently if Scottish MPs votes had not been counted. Some of these votes are important such as the vote on introducing foundation hospitals.

If that might seem reassuring to Labour, it is not. Most of these votes occurred at a time when the party had large majorities. Few expect a Miliband government to have a large Commons majority, so the loss of 40 MPs could be critical in key issues.

He said the previous Labour government had suggested "on the second reading of an English bill, English members could be outvoted by the rest of the UK. So it would be standard practice to have a second vote on a second reading which would allow a period of reflection."

He pointed out that the McKay commission, set up by the government to consider how the Commons might deal with legislation which affects only part of the UK, had proposed an English grand committee comprising solely English members – or if it was an English and Welsh bill, solely English and Welsh MPs – that could amend and return draft legislation before the final vote by all the UK MPs. In either case, English members would have a procedure for their views to be recognised, but in each case the final decision would rest with all MPs in parliament.

The McKay commission, published in March 2013, has not received a full response from the government, partly due to the complexities, such as defining a bill as either England- or UK-wide will not be easy. In a rather woolly compromise, it said: "Decisions at the UK level, with a separate and distinct effect for England (or for England and Wales), should normally be taken only with the consent of a majority of MPs for constituencies in England (or England and Wales)."

But in light of further powers being offered to Scotland, McKay is unlikely to be enough for the Tories – and certainly not enough for Farage, the leader of Ukip. Some Labour voices will demand more. The Labour leader of English local government, Dave Sparks, for instance, in a Guardian interview warned Miliband he would be ignoring this agenda at his peril.

These issues also, incidentally, divide the Liberal Democrats. Danny Alexander, the most senior Scot in the cabinet, said creating "two different classes of MPs" would not work. "There's no party proposing to take away the voting rights of Scottish MPs – that is not part of the agenda. It's not what's going to happen," he said in the final days of the campaign.

Clegg, the Lib Dem leader and Cameron's deputy prime minister, has taken a very different position. "Clearly when you have that degree of devolution [to the Scottish parliament], saying that … a Scottish MP has precisely the same say over matters in English as an English MP, doesn't make any sense. That's why you then decide how you divvy votes in the Commons," he told his regular LBC phone-in audience this week.

Nick Pearce, director of the IPPR, a thinktank that has thought hard about devolution, said on Friday: "Political parties find it impossible to resist the temptation to succumb to party interests on matters constitutional. Labour's deafening silence on the West Lothian question whenever the subject of England is raised, as with recent Conservative calls for an unrestrained form of 'English votes on English laws', are proof enough that the parties have sectional interests that they cannot easily put aside."

He is also right to say: "The constitution-making of recent days might have helped save the union but it is no model for the future. What is needed is a process that replicates, as far as is possible, the passionate democratic conversation that the referendum has provoked in Scotland."

Fortunately, for all the talk of lightning timetables, nothing will happen this side of the election, so all three parties have time to think harder than they have up to this point about England and where it lies in the UK.